Outline
Criminal investigation requires the collection of evidence at the scene of a crime, followed by an analysis of the specimen to come up with evidence. One of the most widely used forms of evidence as fingerprints, which are collected through various techniques and later developed using specific chemicals or optical means. The following term paper discusses different fingerprint detection techniques used by criminal investigating officers and law enforcement agencies. Research areas include a generalized approach to the detection and enhancement of fingerprints and the role of optical techniques. It also includes types of fingerprints that may be collected at the crime scene as well as effects of different types of surfaces such as porous or non-porous on the response of various chemicals.
Introduction
Although in the recent past there has been a lot of advancement in DNA profiling, personal identification is still considered best if it is based on fingerprints during a criminal investigation. According to Henry (2001, p. 57), “for the last 20 years, there has been a great improvement in fingerprint detection as a result of concerted efforts by different research groups on a global scale”. The purpose of this term paper is to explain the current techniques applicable to law enforcement agencies. These techniques are applied in routine detection as well as in enhancing latent fingerprints located on various services.
General Approach
Jones (1993) argues that criminal investigation officers apply optical, chemical, and physical techniques in detecting and enhancing latent fingerprints. However, the best results are achieved if the techniques are applied to follow a logical sequence. Research has shown that detected fingerprints may be increased if several techniques and reagents are applied. A variety of techniques also enhances the quality of already developed fingerprints. Whichever process is applied, it is imperative that a systematic approach is used in a predetermined order. This is because any choice that is incorrect or when only one method has been used is likely to preclude the latter use of other techniques or even reduce its effectiveness. Depending on the prevailing circumstance, best detection techniques depend on factors such as the nature of the surface; on whether it is porous, smooth or rough. It also depends on whether the collected specimen such as blood was contaminated, environmental factors regarding whether the surface was wet or dry as well as the likely age of finger marks collected for evidence.
Any sequence of fingerprint detection should heavily emphasize optical techniques as they do not destroy the fingerprints and are also known to largely improve the results of chemical or physical methods. When other techniques are applied, caution must be observed and developed fingerprints must be recorded at any available opportunity. This is because fingerprints detected through chemical or physical methods are fragile and may easily be destroyed (Henry, 2001).
Optical Techniques
Margot (1994) argues that these techniques make use of specialized light to obtain a simple observation of a specimen under white light. Visible finger marks are disclosed and recorded without further treatment. Optical techniques may also involve complex methods which are able to reveal invisible prints that are hard to develop using other techniques. It is recommended that all fingerprint detection sequences be preceded by optical techniques. If fingerprints have been obtained through either chemical or physical processes, they are enhanced by appropriate optical techniques and this is based on the characteristics of the marks such as luminescence or colour.
Latent fingerprints are usually not luminescent but most modern detection techniques are able to generate luminescent prints. Luminescence is being emphasized because it is highly sensitive in comparison to conventional processes that are used to obtain coloured prints. Luminescence techniques use high-intensity light sources. In the 1980s laboratory-based lasers that were large ad expensive were proposed for this work but today, there are many versatile alternatives that are cost-effective and an example is the filtered arc lamp.
Types of Finger Prints
Research has shown that fingerprints that may be obtained from the scene are classified into three types. First is the moulded fingermark; characterized by fingertip impression, which is 3-dimensional and can be located on malleable substances such as candle wax. Such an impression can be enhanced by the use of oblique lighting. The second type of fingerprint is a visible fingermark that may either be positive or negative. This depends on whether there were contaminations of coloured materials such as blood on the fingers. Other coloured materials such as soot or dust may also have been removed off the surface by the ridges of a fingerprint. It is, therefore, possible to obtain enhancement of the marks by optical means and this largely depends on the properties of contamination. Cases involving blood require specific chemical and optical procedures during enhancement. The last type of fingerprint which is the most common and causes most problems is called the latent fingermark. Most of such marks are usually invisible and therefore require chemical treatment in order to obtain the difference between them and the substrate material. A typical fingerprint of this type comprises a complex mixture made of natural secretions and a variety of contaminants from the surrounding environment. Criminal investigating officers, therefore, require knowledge regarding major constituents in the deposit in order to obtain effective detection of the fingerprint. It is also important for the officers to consider the effects the environmental factors may have on such constituents (Margot, 1994).
Research has shown that latent fingermarks are quite problematic to analyze. It requires the detection of minute quantities of chemical compounds that are specific.
Generally, the least sensitive of the current techniques is fingerprint powders where for a successful detection to be obtained, between 500 and 1000 ng of the powder requires to be used. Deposits of latent fingermarks respond differently to different types of substrates. Furthermore, there are detection techniques known to be effective on particular surfaces but ineffective on others. Because of this problem, it is important for the investigating officers to consider the type of surface before selection is done on the sequence of techniques during fingerprint detection depending on the prevailing circumstances (Jones, 1993).
Fingerprints Involving Porous Surfaces
William (2006) says that, after optical techniques are applied, it follows the method of development depending on whether the surface was dry or wet. If the surface is wet, it means latent fingerprint deposits will be absent if they are comprised of a water-soluble component. The officer, therefore, requires making an efficient choice of a method such as a physical developer. Regarding other cases, applicable techniques such as DFO, metal salt treatment and ninhydrin are recommended. Towards the end of the sequence, one may then apply physical development. The chemical reagent is known as ninhydrin results in the formation of a coloured product called Ruheman’s purple on reaction with amino acids. This chemical was first suggested for fingerprint development in 1954 and has since gained popularity in fingerprint detection involving paper surfaces. During the treatment, the items are dipped in the chemical and then allow the solution to develop the prints between 24 to 48 hours. Research indicates that this method is able to develop prints that are more than 50 years old.
A variety of carrier solvents are used for the chemical but the most successful among all is CFC-113. However, research has shown this substance to be depleting the ozone layer and is, therefore, today not manufactured as a result of it now being prohibited in many countries. Carrier solvents are not supposed to be toxic, flammable or polar. This is purposely meant to minimize the running of ink on documents as well as reduce. The chosen solvent should also not be expensive. It is recommended that alternatives such as hexane and pentane be avoided as they are highly flammable. Acetone is also not recommended because it causes the ink to run excessively on treated documents. Most researchers in various parts of the world have researched CFC- replacements and have come up with HFE-7100 and HFC-4310. There are also several formulations that have been based on the two replacements, which are currently being used. The only disadvantage with the two solvents is that they are expensive and therefore have limited use in most laboratories (Jones, 1993).
At The Crime Scene
According to William (2006), fingerprint detection at the scene of crime generally requires the initial application of optical techniques. This is followed by the transportation of items to the laboratory within the shortest time possible for processing. Suitable development techniques should then be used to treat the remaining surfaces. If the surface is not porous, the best choice is fingerprint powder but for porous surfaces, ninhydrin solution should be used. If the nature of the scene is more serious, it is good to apply chemical techniques such as iodine, as it can develop prints on different semi-porous, porous as well as non-porous surfaces.
Conclusion
Jones (1993) concluded that future prospects of fingerprint detection will involve the replacement of DFO and ninhydrin with indanediones for cases involving porous surfaces. These compounds have the capacity to both ease application of ninhydrin and also enhance DFO’s sensitivity at a lower cost. Researchers are also looking forwards to more use of both on-site as well as chemical enhancement techniques, together with light sources with high intensity through using UV-imaging equipment and digital recording. Such advancement will be possible because of the current information technology. The technology can facilitate both remote and real-time searching of finger marks against fingerprints identification systems that are automated.
References
- Henry C. Advances in Fingerprint Technology, CRC Press (2001) pp56-58
- Jones P. Correlation methods in fingerprint detection studies, Springer (1993)
- Margot P. Fingerprint Detection Techniques, Universite de Lausanne (1994)
- William J. Forensic science: an encyclopedia of history, methods, and techniques, ABC- CLIO (2006)